Light control circuit



Nov. 8, 1932.

I E. o. HULBURT ET AL 1,886,813

LIGHT CONTROL CIRCUIT File d Dec. 23. 1927 5 Sheets-Sheet 1 :ElE i f5 II I a 9" 4 70 Er ==J E |||||||lil- W 0' "A A gmntow Edward flfialbwri mllz'am 1% Crew Nov. 8, 1932. o; HULBURT ET AL 1,886,813

LIGHT CONTROL CIRCUIT v I Filed Dec. 25, 1927 5 Sheets-Sheet 3 I 3110144450445 idwdrd v 0. fialfiuri PVJZZz'am 17 ('retz) V amuesym Nov. 8, 1932 E. o. HULBU-RT ET AL 5,

LIGHT CONTROL CIRCUIT 7 Filed Dec. 23. 1927' s sheets-sheet 4 illllgllk wo uwq Nov. 8, 19 32.. E. o. HULBURT ET AL LIGHT CONTROL CIRCUIT I Filed Dec. 2;. 1927 5 sheets-sheet 5 :E' .u:. i l

I1 Mllll Zlwuemtow 0. flzcliari William H Crew Patented Nov. 8, 1932 UNITED STATES PATENT orl-rca- EDWARD O. HULB'llP-T AND WILLIAM E. CREW, OF WASHINGTON, DISTRICT @F COLUMBIA I LIGHT CONTROL ET Application fled December 33, 1927. serial E0. 242,268.

' variations in the intensity of a source of light.

One of the objects 0 our invention is to provide a circuit arrangement of relatively 'gh sensitivity to changes in light intensity for controlling an indicating element in accordance with the changes in light intensity.

Another object of our invention is to provide an electron tube circuit arrangement with connections to a light sensitive element for controllinga responsive device in accordance with fluctuations in light intensity.

Other and further objects of our invention will be understood from the specification lhereinafter following by' reference to the accompanying drawings in which: i

Figure 1 shows a circuit arrangement employing the principles of our invention; Fig. 2-shows a sim lifiedcircuit arr ement for performin% t e functions of t e circuit shown in ig. 1; Fi 3 shows a modified Ztform of light contro I and circuit arrange-' ment for actuating a responsive device; Fig.

4 shows a simplified circuit arrangement forcarrying out" the principles of operation er the circuit in Fig. .3; Fi 5.is an extended circuit arrangement em odying the rinciples of the circuit shownin Fig. 4; Figs.

'6 and 7 show electron tube oscillator circuits connected with light control circuits in accordance with our invention; Fig. 8 shows a light control circuit in which an external source of oscillations is impressed upon the light controlcircuit; Fig. 9 illustrates an arrangement of electron tube oscillator ar-' ranged externall with respect to the light controll circuit; ig'. 10 shows the arrangement of a photo-electric cell'in the light control circuit of our invention; Fig. 11 shows the arrangement of an ionization chamber in the control circuit in place of the photo-elec-' tric cellshown in Fig. 10; and Fig. 12 illustrates a circuit arrangement for carrying out one application of our invention where a re-' lay system is actuated in accordance with changes in light intensity.

In genera use in commerce and in the plate battery 6 form the oscillatory circuit.

laboratory there are a number of light sensitive devices, some of which because of their mechanical form are properly termed light sensitive cells; others are more properly termed chambers; still others, such as ther-- mocouples, perhaps fall under neither of these categories, although a vacuum thermocouple could certainly be called a light sensitive cell. The light sensitive devices which are employed in the circuit arrangements of our invention are: v

(a) Resistance cells, such as those of selenium, copper oxide, thalium sulphide, and manyothers. These types are usually sensitive in infra-red and visible light and relativel insensitive to ultra-violet light. I

(b Photoelectric cells, such as those of metals, particularl the alkali metals, the alkali metal ,hydri es, etc. types are; usually sensitive in the visible and ultra-vio- 7" let regions-of the spectrum, and less so in the infra-red.

(c) Ionization chambers, are usually sensitive to X-rays and are used. in the spectrophotometry of X-rays. v 75 (d) Thermocouples or the thermopiles, are sensitive throughout the spectrum, but usuallfy are, more used for the longer waves than or the shorter ones.

Our invention in its simplest form consists of a relaxation circuit, one of a general class of'circuits known to the radio art as howling circuits. ,At a sensitive point of the relaxation circuit is attached a light sensitive cell bymeans oia potentiometer circuit.

In carrying out our invention we employ 'an oscillatiufi circuit shown in Fig. 1. The

three electr e vacuum tube 1, together with coils 2 and 3, condenser 4, telephones 5 and The by-pass condenser 7 may or maynot be used as required. If the grid blocking condenser 8 by-passed by a resistance 1' (connecter between points a and b) is introduced, the circuit becomes a relaxation. circuit, a form of 1 c-howling circuit, which when suitably adjusted reduces an audible note, more or less musica in the telephones 5. If the resistance r is changed the quality of the audible note is changed, usually its pitch. So that it 1' is a light sensitive cell, as for example a selenium, or a copper oxide, etc., cell, whose resistance changes when it is exposed to light, the circuit becomes an indicator or detector of light pulses. J

The circuit in Fig. 1 with r constituted by a light sensitive .cell, has a certain degree of sensitivity to light pulses or signals. In order to increase the sensitivity we have introduced the light sensitive cell 10 by means of a potentiometer circuit made of a resistance 11, the cell 10 and a battery 14. An interior point 15 of the battery 14 is connected to the filament and ground (the metal case of the enclosing box). The point 16 between 11 and 10 is connected to the grid at a through the choke 17. The choke is used if necessary. It usual- 1y improves the operation if the 243 circuit oscillates at radio frequency, and in this case the choke is a radio frequency choke. The circuit in Fig. 1 is highly sensitive and its adjustment is relatively simple, permanent and not too critical. The circuit operates well when the circuit 2-4-3 isvaried over a wide range of frequencies, from 10" cycles per either continuously or in steps. Thalofide cells and commercial selenium cells have been used at 10 with success. Batteries 14 and 6 are each about 50 volts to 100 volts, except in y the case of a power tube (7 watts) when a higher voltage is required. The circuit is adjusted to its most sensitive condition by varying 11 and the battery tap 15.

It is seen that the circuit of Fig. 1 contains two batteries 6 and 14. These may be com,- bined into one to give the sim ler circuit shown in Fig. 2 at 18. A r ble set was made up usin the circuit of l ig. 2 and used in field tests. sing a thalofide cell in the set, signals werereceived at night from a 2000 watt tungsten lamp (moving picture projection lamp of a commercial type), screened with a black glass which transmitted only infra-red radiation of a wave length greater than 0.9 at distances up to one-quarter or one-half mile (a conservative estimate), with no focusing mirrors or lenses either on the transmitting lamp or on the receiving cell. The distance at which signals may be received may be increased by the use of focusing devices.

Instead of impressing the potentiometer circuit directly on to the relaxation circuit byv attachment at points a and b, Fig. 1, we have improved the sensitivity by amplifying the potentiometer circuit by means of another standard tube, either a receiving or a power relaxation circuit through the amplifying tube circuit 19-20-21. It is noticed that there are now three separate high pot ential (50 to 100 volts) batteries in the circuit. By making suitable connections these three batteries may be reduced to two. One method by whichthis is accomplished is shown in Fig. 4 where battery 22 takes the place of batteries 6 and 20.

The amplification in thc'potentiometer circuit may be extended further by introducing another stage of amplification. circuit'in which this is done is'shown in Fig. 5, wherein reference character 24 represents an'electron tube constituting an amplifier sta e interposed between the tubes 1 and 19. control resistor 25 is arranged in the output circuit of tube 24 and connects to a suitable potential point on battery- 22. r 1'. I

We have shown-in 6 and 7- modified forms of oscillator circuits whichmay be-employed with the potentiometer control circuit of our invention." 'In Fig.- Y'the oscillator includes electron tube 'lhaving its input circuit completed through inductance 26 and its output circuit completed through inductance 27 with source of. potential =6 and tele'' phones 5 therein; A condenser 28 is provided for facilitating the establishment of oscillations, andthe potentiometer circuit is" conqnected across 'points a and b'whichhas been described in connection-w'iththe previous figureS.

1 :i-. In Fi 7 we haveillustrated both sections 26 and 2%of the inductance which is disclosed in the input andoutputi circuits asshunted by condensers 29 and Y30. The potentiometer clrsuzit 'is connectedwith the same points a an control circuit in which audio frequency oscillations are produced means of genestube -1 through transformer. 32. *The potentiometer circuitmay be connectedwith-points a and b as disclosed'ih connection'=-with':the previous figures.-'-Instead of employing a machine type generator wemay utilize anesator 31, whichfeeds the circuit'of electron '15 cillating tube circuitin the form'of an e1ectron tube system,jasrepresented by'reference character 33 in Fig. 9, where the input and output circuits are coupled-through inductance system .34. tuned by means of condenser 35. The plate circuit may be provided'with a high potential source 36. Theinductance system 34 is' coupled with inductance; 3Z..-in the input circuit ofthe amplifier tube 1, provision being made for the connection ofthe light control circuit across pointsa and b.

plied to the several circuits heretofore illus-' trated in any suitable manner for increasing the amplitude of the control current. We have utilized other control devices beside light sensitive resistance'cells, and Figs. and 11 show the circuit arrangement of our invention employed with a photoelectric cell and a thermocouple.

In Fig. 10 the potentiometer circuit is shown as includin the photoelectric cell 39 including the sensltive surface electrode 40 which is connected to the negative terminal of battery 14 and the collector terminal 41 which is connected to the positive terminal of battery 14. We have used both the alkali hydride photoelectric cell and also the thalofide cell. When using the alkali hydride cell the apparatus is sensitive to visible and ultra-- cell the apparatus. is sensitive to the visible and infra-red light. In order to obtain the highest degree of sensitivity with the alkali hydride cell the voltage at 14 should be. ap-

proximately 150 volts. We have used other commercial photoelectric cells and also sodium cells in glass and with quartz windows.

With the latter type of cell the set is sensitive to the shorter ultra-violet waves which are .transmitted by the quartz but absorbed by the glass. An ionization chamber may be substituted in place of the photoelectric cell 39 in Fig. 10, and with this change the set functions more sensitively to X rays and can be used as a detector and measurer of X rays.

In Fig. 11 we have shown the control circuit arrangement with a thermocouple or thermopile 42 used as the control means. It is not practicable to place the thermocou le directly in the place of the circuit of l ig. 10 because the resistance with usual thermocouples is too low; We have found it necessary to place the thermocouple 42 in the grid circuit of an amplifier 43, the plate circuit of which includes the battery 44 and resistance 45. The output circuit is connected across points a and b of the control circuit of'tube 1. Inductance 17 is connected in one side of the circuit and source of potential 46 in the other side thereof. The circuit has been found to be highly sensitive to long infra-red waves as well as to the shorter ones. I

In the circuits heretofore e lained the response to the light impulses-1s observed by telephone receivers 5 as an audible note. The control circuit may be used to operate a relay for controlling a circuit maker or breaker as represented in Fig. 12.

The output of the control circuit is represented at terminals 50 leading to the input of the audio frequency transformer system 51. The transformer system 51 has its secondary tuned by means of condenser 52 for adjusting the input of the electron tube amviolet light, while with the use of the thalofide plifier 53 to a desired frequency. The potential ugon the grid of the electron tube 53 is contro led from battery 54 and shunt resistance 55. The output circuit of the amplifier tube 53 includes hi h potential source 56, ammeter 57 and the windings 58 of relay 59. A condenser 60 is connected in shunt with the windings 58. Contacts 61 are controlled by the relay windings 58 for opening and closing a circuit to any desired form of load represented generally at 62, which may be in series with potential source 63. The relay is controlled by reason of the effects of variable light upon the light sensitive device 10. Any form of responsive device may be included in the circuit, such as a bell, an indicator, an alarm or other movable device which may change its condition in accordance with the change in effect of light rays upon the lightsensitive cell. p We have found the circuit arrangements described herein highly efficient in operation and while we have described certain preferred embodiments of our invention, we desire that it be understood that no limitations upon our invention are intended other than are imposed by the scope of the appended claim. I

at we claim as new and desire 'to Se cure by Letters Patent of the United States is as follows: i

A light controlled circuit comprising an electron tube having grid, filament and plate electrodes, an input circuit interconnecting said grid and filament electrodes, an out ut 1 circuit interconnecting said plate and lament electrodes, means interlinking said circuits, a light sensitive element, a resistance and a high potential source of energy constituting a looped branch of said input circuit and a choke coil connected to said'looped branch and forming, together with the latter, a series-connection between the 'gridand filament electrodes of said in ut circuit, the respective elements of said light controlled 11o circuit being so disposed in relationto one another that hi h frequency currents are excluded from said looped branch and variations in the intensity of light impinging upon said light-sensitive element are caused 1 to control the grid bias of said electron tube.

In testimony whereof we affix our signa- WILLIAM H. 

